System for amplifying signals generated by a satellite signal generator
unit
The present invention pertains to a system for amplifying signals
5 generated by a satellite signals generation unit.
The satellites amplifying systems, for example coinmunication or
navigation satellites, are used in their zone of optimal efficiency, giving rise,
in fact, to a power response that turns out to be non-linear.
These non-linearities cause power spread (inter-modulation
10 products) that are outside of the useful band, or "spurious", that have to be
filtered at high power, so as to adhere to frequency regulations.
Hence, the implementation of such processing increases and
complicates the payload of the satellite, both in terms of mass and volume.
Techniques are known for linearizing the amplifier by use of signal
15 digital predistortion, at generation of the signal, such as illustrated for
example by the patent US 6 549 067 B1.
Such embodiments impose a high bandwidth for the RF stage or
radiofrequency stage, thus entailing a strong impact in terms of payload of
the satellite.
20 Techniques are also known based on hardware linearizers
carrying out compensation of the non-linearities at the input of an amplifying
device by emulation, in phase opposition of the non-linearities, power-wise,
notably by means of diodes, such as illustrated for example by the French
patent application FR 2 722 350.
2 5 Such embodiments are rather ineffective for the transistor-based
amplifiers commonly employed on satellites.
An aim of the invention is to alleviate the problems cited above.
There is proposed, according to one aspect of the invention, a
system for amplifying signals generated by a satellite signal generator unit,
30 comprising:
- a first pathway comprising a first bandpass digital filter, with finite impulse
response, for filtering outside the useful band, of the digital signals
generated by said unit and a first digitallanalog converter disposed at the
output of said first digital filter,
- frequency transposition means for converting a signal in baseband or in
intermediate frequency into a signal in carrier band, and
- an amplifying device comprising a pre-amplifier and an amplifier,
characterized in that it comprises, furthermore:
5 - a second pathway comprising a second bandpass digital filter with finite
impulse response for filtering outside of its useful band digital signals
generated by said unit, gain means disposed at the output of said second
digital filter, a phase-slaved numerically-controlled oscillator disposed at
the output of said gain means, and a second digitallanalog converter
10 disposed at the output of said numerically-controlled oscillator, and
- a recombiner device for summing the signals of said first and second
pathways.
Such a system makes it possible to concentrate the effectiveness
15 of the method on the frequency band impacted by the phenomenon of nonlinearities,
and not in a global manner as proposed by the existing solutions.
This therefore potentially allows a simplification of the complete chain by
removal of the high-power output filtering.
~ c c o r d i nt~o one embodiment, said frequenzy transposition
20 means are disposed between the output of said recombiner device and the
input of said amplifying device.
In this case, a single frequency transposition and amplifying
device are required at one and the same time for the useful signal and the
compensation signal.
25 In one embodiment, said frequency transposition means comprise
a local oscillator, a mixer adapted for adding frequency-wise, by
multiplication, the input signal of said frequency transposition means and the
output signal of the local oscillator, and a third analog bandpass filter for
isolating the result of said multiplication.
30 According to another embodiment, said frequency transposition
means comprise:
- first frequency transposition sub-means disposed on the first pathway
between the output of said first converter and the input of said summator,
and
- second frequency transposition sub-means disposed on the second
pathway between the output of said second converter (CNA2) and the
I input of said summator.
In this case, the useful bandwidth of the frequency transposition
5 device dedicated to the useful signal (first pathway) may be limited to the
I useful band of the signal.
In one embodiment, said first and/or second frequency
transposition sub-means comprise respectively a local oscillator, a mixer
adapted for adding frequency-wise, by multiplication, the input signal of said
10 frequency transposition sub-means and the output signal of the local
oscillator, and a third analog bandpass filter for isolating the result of said
multiplication.
Thus, the compensation signal may be linearly amplified,. thereby
simplifying the slaving of this compensation. .
15 According to another aspect of the invention, there is also
proposed a method for amplifying signals of a satellite, comprising the steps
consisting in:
- on a first pathway, digitally filtering the signals emitted so as to eliminate
the off-useful-band parts and converting the digital signals obtained into
20 analog signals,
- on a second pathway, digitally filtering the signals emitted so as to
eliminate the off-useful-band parts, applying a gain to the digital signals
obtained, synchronizing said signals in coherence with the signals of said
first pathway, and converting the digital signals obtained into analog
2 5 signals,
- summing the signals of said first and second pathways,
- performing a frequency transposition so as to convert a signal in
baseband or in intermediate frequency into a signal in carrier band, and
- amplifying the signals before emission.
30
The invention will be better understood on studying a few
embodiments described by way of wholly non-limiting examples and
illustrated by the appended drawings in which:
- Figure 1 schematically illustrates an embodiment of a system for
amplifying signals generated by a satellite signals generation unit, according
to one aspect of the invention; and
- Figure 2 schematically illustrates another embodiment of a
5 system for amplifying signals generated by a satellite signal generation unit,
according to one aspect of the invention.
In all the figures, elements having the same references are similar.
Figure 1 schematically represents a system SA for amplifying
10 signals generated by a signal generation unit UGS of a satellite. The
amplifying system SA comprises a first pathway V l furnished with a first
band.pass digital filter F1 with finite impulse response for filtering outside of its
useful band digital signals generated by the unit UGS, and a first
digitallanalog converter CNAI disposed at the output of said first digital filter
15 F1. The amplifying system SA also comprises a frequent-y transposition
module MTF for converting a signal in baseband or in intermediate frequency
into a signal in carrier band, and an amplifying device DA comprising a
pre-amplifier and an amplifier.
The amplifying system SA comprises, furthermore, a second
20 pathway V2 comprising a second bandpass digital filter F2 with finite impulse
response for filtering' outside of the useful band, digitally generated by the
unit UGS, a gain module G disposed at the output of said second digital filter
F2, a phase-slaved numerically-controlled oscillator NCO disposed at the
output of the gain module G., and a second digitallanalog converter CNA2
25 disposed at the output of: the numerically-controlled oscillator NCO, and a
recombiner device S .for summing the signals of the first and second
pathways V1, V2.
The frequency transposition module MTF is disposed between the
output of the recombiner device S and the input of the amplifying device DA.
30 In this instance, the frequency transposition module MTF
comprises a local oscillator OL, a mixer MEL adapted for adding frequencywise,
by multiplication, the input signal of the frequency transposition module
MTF and the output signal of the local oscillator OL, and a third analog
bandpass filter F3 for isolating the result of said multiplication.
The local oscillator OL defines the carrier frequency at which the
recombined signal will be modulated. The analog bandpass filter F3 makes it
possible to limit the input of the amplifying device DA to the useful band of
the signal, including the compensation.
5 The embodiment of Figure 1 exploits the optional ability of the
module MTF to manage at one and the same time the useful signal and the
compensation signal.
Figure 2 schematically represents a system SA for amplifying
signals generated by a unit for generating signals UGS of a satellite. The
10 amplifying system SA comprises a first pathway V1 furnished with a first
bandpass digital filter F1 .with finite impulse response for filtering outside of
the useful band digital signals generated by the unit UGS, and a.'first
digitallanalog converter CNAl disposed at the output of said first digital filter
F1. The amplifying system SA also comprises a frequency transposition
15 module MTF for converting a signal in baseband or in intermediate frequency
into a signal in carrier band, and an amplifying device DA comprising a
pre-amplifier and an amplifier.
The amplifying system SA comprises, furthermore, a second
pathway V2 comprising a second bandpass digital filter F2 with finite impulse
20 response for filtering outside of its useful band digital signals generated by
the unit UGS, a gain module G disposed at the output of said second digital
filter F2, a phase-slaved numerically-controlled oscillator NCO disposed at
the output of the gain module G, and a second digitallanalog converter CNA2
disposed at the output of the numerically-controlled oscillator NCO, and a
25 recombiner device S for summing the signals of the f k t and second
pathways V1, V2.
The frequency transpositi'on module MTF comprises a frequency
transposition module MTF comprising:
- a first frequency transposition sub-module MTFI disposed on the first
30 pathway V1 between the output of the first converter CNAl and the input
of the summator S, and
- a second frequency transposition sub-module MTF2 disposed on the
second pathway V2 between the output of the second converter CNA2
and the input of the summator S.
The first andlor second frequency transposition sub-modules
MTFI, MTF2 comprise respectively a local oscillator OLI, OL2, a mixer
MELI, MEL2 adapted for adding frequency-wise, by multiplication, the input
signal of the frequency transposition .sub-modules MTFI , MTF2 and the
5 output signal of the local oscillator OLI, OL2, and a third analog bandpass
filter F3-1, F3-2 for isolating the result of said multiplication, thereby making
it possible to limit the spectral occupancy of the signals at the input of the
amplifying device DA.
The embodiment of Figure 2 simplifies the slaving in terms of gain
10 and synchronizatio'n of the compensation signal.

CLAIMS
1. A system (SA) for amplifying signals generated by a unit
(UGS) for generating signals of a satellite, comprising:
- a first pathway (VI) comp,rising a first bandpass digital filter (FI) with
. . finite impulse response for filtering outside of its useful band digital
signals generated by said unit (UGS) and a first digitallanalog
converter (CNAI) disposed at the output of said first digital filter (FI),
- frequency transposition means (MTF) for converting a signal in
baseband or in .intermediate frequency into a signal in carrier band,
and
- an amplifying device (DA) comprising a pre-amplifier and an amplifier,
characterized in that it comprises, furthermore:
- a second pathway (V2) comprising a second bandpass digital filter (F2)
with finite impulse response for filtering outside of its useful band digital
signals generated by said unit (UGS), gain means (G) disposed at the
output of said second digital filter (F2), a phase-slaved numericallycontrolled
oscillator (NCO) disposed at the output of said gain means
(G), and a second digitallanalog converter (CNA2) disposed at the
output of said numerically-controlled oscillator (NCO), and
- a recombiner device (S) for summing the signals of said first and
second pathways (V1 , V2).
2. The system (SA) as claimed in claim 1, in which said
frequency transposition means (MTF) are disposed between the.:outpuf of
said recombiner device (S) and the input of said amplifying device (DA).
3. The system (SA) as claimed in claim 2, in which said
frequency transposition means (MTF) comprise a local oscillator (OL), a
mixer (MEL) adapted for adding frequency-wise, by multiplication, the
input signal of said frequency transposition means (MTF) and the output
signal of the local oscillator (OL), and a third analog bandpass filter (F3)
for isolating the result of said multiplication.
4. The system (SA) as claimed in claim I, in which said
frgquency transposition means (MTF) comprise:
- first frequency transposition sub-means (MTFI) disposed on the first
pathway (VI) between the output of said first converter (CNA1) and the
5 input of said summator (S), and -- *- *% *-.;*-, +-+-*,* *-
- second frequency transposition sub-means (MTF2) disposed on the
second pathway (V2) between the output of said second converter
(CNA2) and the input of said surnmator'(S).
, 10 5. The system (SA) asclaimed in claim4, in which said first
andlor second frequency transposition sub-means ' (MTFI, MTF2)
comprise respectively a local oscillator (OLI, OL2), a mixer (MELI, MEL2)
adapted for adding frequency-wise, ,by multiplication, the input signal of
said frequency transposition' sub-means (MTF1, MTFZ) and the output
15 signal of the local oscillator (OLI, OL2), and a third analog bandpass filter
" (F3-1, F3 - 2) for isolating the result of said multiplication..
6. A method for amplifying signals of a satellite, comprising
the steps consisting in:
, .
20 - on a first pathway (VI), digitally filtering (FI) the signals emitted so as.
to eliminate the off-useful-band parts and converting (CNAI) the di&t&l
. . CLj'
signals obtained into analog. signals, '
- on a second pathway (V2), digitally.filtering (F2) the signals emitted so
. , as to eliminate the off-useful-band parts, applying a gain (G) to the
25' digital signals obtained, synchronizing said signals in coherence with
the 'signals of said first pathway,. and converting (CNA2) ' the digital
-signals obtained into analog signals,
.,. . . , . . _ . - summing (S) the signals of said first and second pathways (VI, V2),
' - performinga frequency transposition (MTF) so as to convert a signal in
30 baseband or in intermediate frequency into a signal in carrier band, . . . . . , :
.. .-.
and
- amplifying (DA) the signals before emission.